How agriculture and forestry change climate, and how we

How agriculture and forestry change climate, and how we

How agriculture and
forestry change climate,
and how we deal with it
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How agriculture and
forestry change climate,
and how we deal with it
2
3
Publisher
Karlsruhe Institute of Technology (KIT)
Institute of Meteorology and Climate Research
Atmospheric Environmental Research (IMK-IFU)
Prof. Dr. Almut Arneth
Division of Ecosystem-Atmosphere Interactions
Kreuzeckbahnstr. 19
82467 Garmisch-Partenkirchen
Germany
www.luc4c.eu
Editor, design and layout:
Dr. Mechtild Agreiter
KIT/IMK-IFU
Garmisch-Partenkirchen 2015
The project LUC4C has received funding from the European Union’s Seventh
Framework Programme for research, technological
development and demonstration under
grant agreement number 603542.
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Contents
1.
Land-use change: what is it, and why does it affect cli-
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mate change?
2.
Land-use change in international climate policy
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3.
Models and methods for analysing LUC-climate change
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interplay
4.
What are socio-economic emission scenarios and what
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are they good for?
5.
The interconnected web of food production, climate
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and society
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6.
Bioenergy, land-use change and climate
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7.
How will land-based sectors adapt to climate change?
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8.
Sustainable land use: Elinor Ostrom‘s alternative
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This booklet was developed as part of the project
LUC4C, Land-use change: assessing the net climate
forcing, and options for climate change mitigation and
adaptation, funded by the EU. More information can
be found on the project website www.luc4c.eu.
In this booklet we have gathered articles about the
interaction of land-use change and climate change,
climate policy, the state of the art of climate models
and scenarios, the connection to food production
and the interaction with human societies.
The aim of LUC4C is to bring forward our knowledge about the interactions of climate change and
land-use change. The scientists in LUC4C work on
the development of complex earth system models, tools for providing an integrative assessment of
the land-use change - climate change interplay, and
guidelines for policy and other societal stakeholders. LUC4C seeks to identify and understand the
societal and environmental drivers of land-use and
land cover change (LUC), as well as why they are
relevant to climate change. The project evaluates
different mitigation and adaptation policies in view
of how they affect important ecosystem processes,
and whether (unintended) conflict with other ecosystem services related to LUC arise from the implementation of such policies.
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1
Land-use change: what is it,
and why does it affect climate
change?
Almut Arneth
People have been transforming natural ecosystems
to grow food, and to obtain firewood and timber,
for millennia. Today, about 40% of the ice-free land
surface is covered by crops or pastures, and in many
parts of the world we continue to expand these areas because the world’s population is growing, and
this growth requires resources we obtain from the
land.
When investigating the effects of transforming natural ecosystems, scientists often distinguish land-cover change from land-use change. Land-cover change
describes the transformation of an ecosystem type,
for instance the replacement of a natural forest or
natural grassland with agricultural crops. Land-use
and land-use change describes the way that crops,
pastures, or forests are managed. This can include
a change in the amount of fertiliser or irrigation
applied, or animal grazing density, or a change in
the tree species composition of a managed forest.
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Land-cover change and land-use change both interact with climate change, and in this booklet we will
not differentiate between the two; it is, however, important to be aware that both are aspects of what is
termed here solely “land-use change”.
Land-use change has many effects on climate change.
The best known of these are identifiable via the
greenhouse gas content of the atmosphere. Greenhouse gases like carbon dioxide (CO2), nitrous oxide
(N2O) and methane (CH4) affect the earth’s climate
and these gases have increased in the atmosphere
due to human activities, especially over the last 100200 years. The greenhouse gas concentration in the
atmosphere can be measured directly from a set
of observation stations around the world, but also,
for instance, in air-bubbles trapped in glaciers – and
these air bubbles can give us a very good record
of greenhouse gas levels hundreds and thousands of
years ago.The exact chemical signature of the greenhouse gas molecules (the so-called isotopic composition) helps to identify human activities as the main
source for this increase.
When forests are replaced by pasture or crops, a
large amount of CO2 enters the atmosphere, most
of it directly (if the forest is burned), or over the
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ensuing years (when the wood products are out of
use and are subsequently burned or beginning to
decompose). A lot of carbon is stored in the tree
stems, but in addition the remaining tree roots die
and are decomposed to CO2 by soil organisms.
Since crops and grasses do not have stems, and have
less root biomass than trees, agriculture and pasture ecosystems contain less carbon in total than
a forest – carbon is thus “lost” to the atmosphere
upon deforestation. Carbon can also be “retaken”
from the atmosphere if forests replace crops, but
the area, globally, where forest increases is relatively
small. It has been estimated that around one third
of the total anthropogenic CO2 in the atmosphere
today originates from land clearance over the last
decades to centuries.
Like CO2, N2O and CH4 are important greenhouse
gases. Around 50% of the N2O that can currently be
measured in the atmosphere may originate from agriculture, mostly from fertiliser use. Nitrogen-containing fertiliser is partially taken up by plants, to
support growth. Part of it, however, remains in
the soil, where microbes transform it into various
N-containing gases, including N2O, which then diffuses back into the atmosphere. CH4 is also a by-product of soil microbial activities in rice paddies, pro14
duced by so-called methanogens. These microbes
use dead plant material to “feed” themselves and
to grow in conditions of low oxygen (found in rice
because it is often grown in flooded soils), and CH4
is the end-product of their metabolism. And, CH4 is
produced in the stomachs of ruminants, particularly
cows. At present, rice paddies and livestock jointly
contribute nearly half of the total annual man-made
methane emissions.
These greenhouse gas emissions contribute to climate warming. Their effect is important for climate
globally, because these gases are chemically low-reactive and long-lived, and therefore have plenty of
time to become mixed in the atmosphere. They remain in the atmosphere for decades to many centuries, until they are eventually removed by physical or
chemical processes.
Land-use change also affects climate by processes unrelated to the emission of greenhouse gases.
These processes are often summarised as “biophysical”, and they operate by affecting radiation and
evapotranspiration. In short, when sunlight hits the
land surface, a proportion of this light is directly reflected back to the atmosphere, and the remainder
is absorbed. The amount of reflection is called albe15
do, and the albedo of a dark surface is lower than
that of a light surface. A forest landscape, therefore,
has a lower albedo than a cropland or grassland, and
this affects the forest’s surface temperatures, as the
absorbed sunlight is turned into heat. In ecosystems
that are managed for food production, more sunlight
is reflected compared to a forest, and thus their land
surface temperature is relatively lower than that
above a forest.
es, but in other regions, land-use change can even
yield a local cooling.
It is important to mention here a third effect of
land-use change, beyond the aforementioned longlived greenhouse gases and biophysical processes.
This is not where the story ends, however, because
the absorbed radiation is only partially turned into
heat; another part is used to move water vapour
from ecosystems into the atmosphere. This process
is known as evapotranspiration, and consists of water vapour loss from soils (evaporation) and from
plants via their green leaves (transpiration). High
evapotranspiration leads to cooling.
Whether or not a natural forest ecosystem will have
higher rates of evapotranspiration than a crop or a
pasture system is difficult to say: it depends, for example, on the global region in which the plants grow,
the rooting depth of the natural versus the managed
vegetation, and whether or not the crop is irrigated. In some regions, the occurrence of droughts has
been linked to biophysical land-use change process16
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Land-use change is also an important consideration
in relation to emissions of trace gases that act as
a precursor to the formation of ozone in the lower parts of the atmosphere. In the lower air layers,
ozone is a greenhouse gas which contributes to climate warming. Finally, aerosols and their precursors
are also climate-change agents, with either a warming or cooling role. In contrast with greenhouse gas
emissions, the effects of biophysical processes and
of reactive trace gases and aerosols are therefore
mostly restricted to the region where the change
occurs, and can either contribute to a warming or
cooling effect.
Carbon
dioxide
Nitric
oxide
Sunlight
Water
vapour / warmth
/
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Methane
Carbon
dioxide
Nitric
oxide
Sunlight
Water
vapour / warmth
Methane
/
Climate-relevant exchanges between the land surface and the atmosphere.
Opposite page: In a pristine landscape, there is on average no (or little)
net uptake or loss of the greenhouse gas CO2, Photosynthetic carbon
uptake and losses of carbon through (for instance) respiration and fire
are in balance. Small sources of the greenhouse gases methane and nitrous oxide exist, in particular in wetlands and savannahs. A comparatively larger proportion of sunlight, compared to croplands, is absorbed
at the land surface. More of the energy available via this absorption is
used for transpiring water vapour.
This page: In a landscape used by humans, CO2 is emitted by land-use
change, while emissions of methane (through rice paddies and life-stock)
and nitrous oxide (through use of fertiliser) greatly exceed emissions of
these greenhouse gases in natural ecosystems. A comparatively smaller
proportion of sunlight, compared to natural ecosystems, is absorbed by
the land surface. Often, more of the energy available via this absorption
is used to heat the land surface.
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These many climate-related aspects of land-use
change, and the fact that they operate over different
scales of time (days to centuries) and space (regional to global), pose a large challenge when aiming to
understand all the effects of past, present and future
land-use change on climate. Furthermore, emissions
and biophysics are not only determined by the way
we use our land, but actually respond to climate
change themselves; warmer temperatures will enhance the underlying biological and chemical processes, leading to enhanced emissions and biophysical processes. In this way, they feed back to climate
change.
But does climate change also affect land use and
land-use change? Clearly so; climate in a given region
is an important determinant of the type of food or
timber grown there, as it determines the available
water for irrigation, and impacts yields (through, for
example, droughts, floods, and frost). Climate change
will thus affect harvests, both locally and regionally,
either positively or negatively, which is one factor
that influences how people choose to manage land.
Climate is, nonetheless, only one aspect of such decisions, and other factors, such as economic, social
or political change, are fundamental to the understanding of land-use change.
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2
Land-use change in
international climate policy
Joanna House & Annalisa Savaresi
Policies and decisions on how land is managed affect greenhouse gas emissions. International policy
to measure and manage greenhouse gas emissions
from the land sector has gradually been put in place.
Virtually all states in the world have ratified the 1992
United Nations Framework Convention on Climate
Change (UNFCCC), which requires them to:
• adopt national policies to limit anthropogenic emissions of greenhouse gases, and protect,
maintain and enhance greenhouse gases storage
in sinks and reservoirs
• periodically publish national inventories of
greenhouse gas emissions and sinks using agreed
methodologies
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The so-called land use, land-use change and forestry (LULUCF) sector includes emissions and storage
associated with conversions between land categories (e.g. from forest land, to cropland, from wetland
to settlements, etc.) and as a result of activities on
managed land within a category. Developing definitions and methodologies for LULUCF activities in
international climate law has been a long and complex process. Two particularly difficult issues have
been how to deal with: (a) permanence (e.g. a newly
established or existing forest may be vulnerable to
future human activity or environmental change, disease, fire, etc.); and (b) leakage (e.g. protecting or
establishing a forest in one place may lead indirectly
to forest being cut for agriculture in other places).
Further difficulties have arisen from the fact that in
some countries, like Australia or New Zealand, the
LULUCF sector is a large greenhouse gas source,
as a result of intensive cattle grazing and associated
emissions of methane (see chapter 1). By contrast, in
other countries the LULUCF sector is a greenhouse
gas sink, for instance when crop areas are converted
back into forest (like in many EU member states),
or countries that may have large potential to avoid
future deforestation (like in Brazil).
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Forests 40
0
−1000
−2000
−3000
South America
Africa
Europe
North America
−4000
−5000
1990−2000
2000−2005
2005−2010
Global land area used (%)
Change in Forest Area (x1000 ha/year)
1000
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Agriculture Cropland
Pasture land
30
25
20
15
10
5
0
1850
1900
1950
2000
Climate Policy Land-use change contributes to climate change, and hence affects climate policy. But land use can also offer opportunities to mitigate climate
change through appropriate policies.
Top left: Change in forested area (in 1000s hectares per year) for selected regions (source: Forest Resources Assessment, 2010). Tropical
regions are still undergoing strong deforestation, whilst in some areas
of Europe and North America the forest area expands, following e.g.,
abandonment of agricultural land.
Top right: Fraction of global land area used for either cropland or pastures (Klein Goldewijk et al. 2011, Glob. Ecol. Biogeogr. 20, 73–86).
Conversion of natural land into cropland has increased historically very
strongly, but with a declining trend over the last few decades.
Most parties to the UNFCCC have also ratified the
1997 Kyoto Protocol, which set legally binding emissions reductions targets for some developed countries for the period between 2008 and 2012. After
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lengthy negotiations, a somewhat smaller group of
developed countries undertook a new set of emission reduction targets for the period between 2013
and 2020. Under the Kyoto Protocol, developed
countries may use LULUCF activities to meet their
targets. Accounting for emissions and removals from
afforestation, reforestation, deforestation and forest
management is mandatory, whereas countries can
choose whether or not to account for other landbased emissions, such as cropland, grazing land and
wetland management.
Developing countries can also participate in emission reduction activities in the land sector. Under
the Clean Development Mechanism, some LULUCF
activities (limited to afforestation and reforestation)
can be performed in developing countries with finance provided by developed countries, which can
then claim the resulting greenhouse gas reduction
credits. More recently, developing countries were
also given the possibility to access finance to carry
out afforestation, reforestation, prevention of deforestation and forest management under REDD+
(Reducing Emissions from Deforestation and forest Degradation including conservation, sustainable
management of forests and enhancement of forest
carbon stocks).
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Many developing countries have furthermore made
pledges for voluntary emission reductions in the
LULUCF sector, such as:
• Brazil proposes to reduce emissions by around
one-third compared to the “Business as Usual
emissions” in 2020, including reducing deforestation in the Amazon region by 80% between
2020, compared to the year 2005.
Parties to the UNFCCC are in the process of negotiating a new climate agreement, which is expected
to be adopted at the Paris Climate Change Conference in December 2015. The new agreement may
include a dedicated REDD+ mechanism and new
rules on land-use change, and possibly even legally
binding obligations for some developing countries
to reduce their emissions from LULUCF activities.
• China pledged to increase forest coverage by 40
million hectares and forest stock volume by 1.3
billion cubic metres by 2020, compared to the
situation in 2005.
• Indonesia seeks to cut emissions by 26% to 41%
by 2020 compared to ”Business as usual emissions”. Presently, about 80% of Indonesia’s total emissions come from deforestation and peat
fires.
• Mexico wants to reduce emissions by 30% below ”Business as usual” by 2020, including programmes of REDD+ and afforestation.
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3
Models and methods for
analysing LUC-climate change
interplay
Nathalie de Noblet-Ducoudré
Measuring the impacts land-use change has on the
atmosphere (and climate), with regard to greenhouse gas content, other land-use change-related substances, and heat and water, is challenging.
One option would be to perform measurements at
two experimental sites that have initially the same
weather, with one of these sites then exposed to a
land-use change. In this way, one can compare the
situation in the “pristine” and the “disturbed” location. In practice it is, however, very difficult to find
suitable locations that would allow for such types of
controlled experiments. Moreover, a local distortion
may not be sufficient, as the changes caused in the
atmospheric state and/or composition at the disturbed site can also lead to changes in atmospheric
motion (and hence the weather), which would also
then influence the pristine location. The difficulty
(or even the impossibility) of measuring the climate
impacts of land-use change in situ has led to the
development of models. These models are mathematically representative of our knowledge of how
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the given subject functions, enabling us to compare
the differences between two contrasting situations,
and helping us to explore how land-use change and
climate change will interact in the future (or how
they have done so in the past).
To account for the full interplay, we need three
models. These models are interconnected in that information produced by one model is then used by
another:
• The global climate model calculates the exchanges of heat, energy, water, greenhouse gases and other chemical compounds between the
terrestrial & oceanic biospheres and the atmosphere, the flow of water from continents to
oceans, the atmospheric winds & oceanic currents, and the chemical/physical/thermal state of
the atmosphere. In order to assess how climate
changes over time, for instance in response to
human activities such as fossil fuel combustion,
the climate model is fed with: a) atmospheric
concentrations of greenhouse gases and aerosols, from both natural and anthropogenic
sources, and b) the geographical distribution of
land ecosystems and information regarding their
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uses (whether they are irrigated or not, harvested or not, etc). Changes in land use are provided
as inputs to the climate model which then produces as outputs the land-use change-induced
alterations in climate (diurnal and seasonal fluctuations of temperature, rainfall, wind, etc.).
• The dynamic global vegetation model
(DGVM) mimics the functioning of the terrestrial biosphere. It embeds a representation of
natural and managed ecosystems, and calculates
the biosphere’s life cycle: plant photosynthesis,
respiration, plant growth and competition for
water, sunlight and nitrogen. In geographic locations with managed ecosystems, irrigation and
fertilizer can be applied, and annual crop yields
calculated. The DGVM needs a set of atmospheric variables that comes from the climate
model (for instance radiation, air temperature
and humidity, CO2 concentrations, rainfall, wind)
that are needed to drive the biosphere’s functioning. As for the climate model, alterations in
land-use change are provided as inputs to this
DGVM.
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• The land-use model (LUM) is applied to
study how humans have used the planet for
agriculture and for pasture. Land-use change
models take into consideration changes in human population density, as well as income levels, estimates of how technology develops and
also people’s lifestyles (for instance, a preference for certain food types). A representation
of general economic principles is combined
with social and natural system constraints (like
the amount of yield that can be achieved in
a certain region, due to the local climate and
soils, e.g., from the DGVMs). These models
also require information about the foreseen
development of human societies (see chapter
4), and simulate changes in land use that are
needed by the climate and vegetation models.
Presently, Integrated Assessment models are
typically used to provide the required landuse change projections in the drawn modelling
framework (chapter 4), but there are also alternative LUM approaches under development
that seek to consider in more detail the human
decisions that lead to land-use change.
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Integrated
Assessment
Model
Fossil fuel emissions
of greenhouse gases
and other climaterelevant substances
Emissions from LUC
Climate Model
(Includes BiosphereAtmosphere
Interactions)
Change in
cropland,
grassland and
forest area
Adaptation of LUC
to changes in yields
and management
Land Use Model
(Also accounts
for socio-economic
changes)
Climate effects
on ecosystems
Dynamic
Global Vegetation
Model
(Includes Crop Model)
Yields, impacted by
management (e.g. irrigation,
fertiliser, crop variety) and
climate change
The Figure shows information flow between the various sub-models
that are used to assess the land-use change - climate change interplay.
Green text summarises the information produced by the individual
models, black arrows show the direction of how this information is
passed between the models.
Alterations in land-use change simulated by the
LUM affect climate, for example through changes in
greenhouse gas emissions, or surface characteristics
such as albedo (see chapter 1). Those changes are
taken into account by the climate model, and impact
fluxes such as water, energy, and heat, at the biosphere-atmosphere interface, and thereby climate.
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4
What are socio-economic emission
scenarios and what are they good
for?
Detlef van Vuuren & Elke Stehfest & Alexander Popp
Given the inertia in the climate system, it is important to assess the potential long-term consequences of decisions made today. Scenario analysis has
been developed as a tool to explore and evaluate
the extensive uncertainties associated with possible
future developments. For instance, these scenarios can combine assumption on the growth of the
earth’s human population, economic and technological development and trade patterns. In recent
years, the need for scenarios that integrate across
the different climate change research communities
has become clear.These scenarios allow us to bridge
research into understanding the climate system, into
climate-change impacts, adaptation and vulnerability, and into future anthropogenic greenhouse gas
emissions and options for mitigation. The emissions
from these scenarios are, for instance, used in the
model-framework explained in chapter 3. Currently,
these scenarios are organized around two important dimensions: the representative concentration
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pathways (or RCPs) describe a range of possible
emissions pathways leading each to a specific level
of radiative forcing, which determines the amount of
climate change, and the associated climate-change
impacts. The possible future socio-economic conditions that correspond to individual RCPs are then
described in the shared socio-economic pathways
(SSPs).
Land use plays a key role in these scenarios. The
SSPs provide five alternative stories of future socio-economic development, including possible
trends in agriculture and land use. Such SSPs could,
for instance, describe a future world of investment
in environmental technology, low population growth,
high standards of education, and reduced economic
inequality. Another SSP might follow a future path
that is not very different from history, including continued population growth and fossil fuel burning. In
each of the SSPs, climate policies can be introduced
to reduce emissions to reach concentration levels
consistent with the RCP scenarios. Land use related
policy measures play an important role in this, including, for instance, the use of bioenergy, measures
related to forestry, and reducing non-CO2 greenhouse gas emissions from agriculture.
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What models are used to develop the RCPs
and SSPs?
Future emissions are a function of complex
interaction between all kinds of socio-economic
factors, including population dynamics, economic
development, technological change, cultural
and institutional changes, and policies. So-called
integrated assessment models (IAMs, see chapter
3) have been developed as a consistent framework
to study possible future pathways for these drivers,
concentrating on energy and agriculture/land-use
systems and associated emissions.
Land use futures are uncertain
Different studies in the past have looked into potential land-use futures. Most of these projections
indicate that in the next few decades the area and
agriculture continues to grow slowly, driven by an
increase in demand for food and fodder outpacing
the simultaneous expected increase in agricultural
yields.
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The graph shows worldwide LUC emissions (in equivalents of CO2)
of the scenarios in the AR5 IPCC database for a baseline (“business as
usual”) scenario compared with a scenario that aims at climate change
not exceeding 2 °C (shaded red and green areas are due to a range of
IAM output that represents the scenarios). The corresponding RCPs
(RCP8.5 and RCP2.6) are drawn as lines. Reducing the land-use related emissions can contribute to climate policy, such as achieving the
2-degree target, but it is also clear that it is not possible to bring these
emissions to zero. (Data based on IPCC AR5-WG3 Scenario database
and RCP scenarios)
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The degree of land-use expansion depends on uncertain trends in population growth, dietary changes, possible demand for non-food products such as
bioenergy and future developments in agricultural yields (in turn being determined by technology
and environmental impacts, such as climate change).
Over time, these uncertainties may result in very different land-use change patterns. Many scenarios, in
fact, show a stabilization of land use in the absence
of climate policy.With climate policy (see chapter 2),
however, future demand for bioenergy may lead to a
further “claim” on fertile agricultural land.This could
result in a further loss of natural areas, but also in
higher agricultural yields in response to land scarcity.
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The climate impacts are obviously also uncertain.
While in the past few years model-based studies
have started to explore the biochemical impacts of
land-use change under different scenarios, the exact
changes in the earth’s carbon cycle are still unknown.
Moreover, the biogeophysical impacts of future landuse change, such as those related to absorption and
reflection of light (see chapter 1 and 3), have not
often be studied and can be strong at a local scale.
Coupling IAM models, biophysical models, such as
DGVMs, and climate models, as done in LUC4C,
allows us to explore the relevant relationships between land use and climate change in a unique way.
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5
The interconnected web of food
production, climate and society
Thomas Pugh
All organisms modify the environment around them
to better suit their needs, but ever since the birth
of agriculture around 10 000 years ago, humans have
been doing so quite profoundly. Agricultural systems
can differ markedly from the ecosystems they replace, in the most extreme cases replacing biodiverse forests with large expanses of monoculture
crops. As stated already earlier in this booklet, 12%
of the global land surface is occupied by cropland,
with a further 25% used for grazing. Overall, approximately 25% of the sun’s energy captured by plants
is now appropriated for human use.
The area of cropland required to support human
societies depends on the human population reliant
on it, their dietary preferences, and the productivity
of the cropland. Cropland coverage has increased
greatly with the dramatic rise in global population
over the last 500 years but, more recently, much of
the required increase in food production has been
met by modern farming practices, such as fertilisation, mechanisation, breeding of more productive
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crop types, and suppression of natural pests. Many
projections of how the global population will be fed
in the 21st century (see chapter 4) are based on the
idea that technological advances will continue at the
rate of the last half century, or that places where
these advances have not yet been effectively implemented, often developing countries, can realise large
increases in agricultural production through transfer
of these technologies. It is far from clear, however, if
these projections and their underlying assumptions
are realistic.
Temperature increases or changes in rainfall as a result of climate change can have a profound effect on
crop growth. In addition to the obvious effects of
drought, heat-waves during the flowering stage can
substantially reduce the yields of grain crops. Furthermore, extreme weather events such as floods
or hailstorms, which are expected to increase in
intensity under climate change, can destroy crops
in the field. The combination of these factors can
act both to reduce crop yields, and to make them
less reliable. As is so often the case, these negative
effects are not expected to be spread equally across
the globe, but are instead concentrated in tropical
regions, where crop production is often already
marginal.
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It is not all bad news, however; croplands in much
of the middle latitudes are actually expected to
become more productive as a result of increasing
temperatures lengthening the growing season. Furthermore, whilst carbon dioxide drives increases in
temperature, there is abundant evidence to show
that it also increases the rate at which plants photosynthesise. It is thus possible that increases in crop
yield due to the direct effect of carbon dioxide on
plants could counterbalance the decreases in yield
due to the effect of carbon dioxide on climate.
Carbon dioxide also reduces the water requirements of crops, something that may be very important in arid regions, or those regions likely to become
arid under a changing climate. The overall effect of
carbon dioxide and climate change on crop yields is,
however, very uncertain. Experiments show a mixed
response, and no-one knows for sure how yields will
respond. There are also questions over whether increased carbon dioxide will change the quality of
crops; there is some evidence that it may decrease
the protein and mineral content.
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Clearly, climate-driven changes in crop production
will have a strong bearing on the amount of cropland required, and where it would best be located.
In the face of falling yields, agricultural expansion
or re-location of croplands may be the only way to
increase food production, yet there is little unused
land on this planet. Moving or increasing cropland
area will always come at the cost of some other
function provided by ecosystems, for instance carbon storage (see chapter 1). Natural ecosystems
store huge amounts of carbon, twice to three times
the amount in the atmosphere. Although there are
some exceptions, croplands tend to store less carbon in both vegetation and soils than the natural
systems they replace. The harvesting of crops removes material that would otherwise end up stored
in the soil. In addition, processes such as tillage open
up the soil structure, increasing both the likelihood
of soil erosion, and the rate at which carbon-containing substances in the soil are decomposed into
carbon dioxide. The actual amount of carbon lost
varies with climate, crop, soil type and farmer choices. For instance, farming methods which avoid tilling,
and which leave the non-food part of the crop on
the field, can greatly reduce such losses.
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These effects of agriculture on greenhouse gases
can even lead to feedback effects; reductions in crop
yields due to climate change, for instance, may lead
to cropland expansion, reducing carbon storage and
increasing emissions of other greenhouse gases, and
thereby increasing climate change, which in turn
further decreases crop yields. The opposite is also
possible. Therefore, in order to understand human
land-use requirements in the future, it is critical to
understand how crop production will evolve under climate change and associated socio-economic
changes. But simultaneously, to understand climate
change, we must also know how croplands will expand or contract, or how their management will
change.
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There are also questions of whether socio-economic systems are able to transport food from where
it is best produced to where it is most required, or
whether economic realities may dictate a course of
agricultural land use that does not follow the theoretically-optimal path. The fundamental interconnection of these many human and natural systems
poses a huge challenge to researchers. Unravelling
this complex picture is key to understanding how to
adapt to the unavoidable effects of climate change,
and how to effectively mitigate against the most extreme changes. Without such a holistic understanding, efforts to maintain our food supplies or to limit
climate change to a reasonable level will rely more
on luck than judgement.
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6
Bioenergy, land-use change and
climate
Almut Arneth & Kerstin Baumans
The term ‘bioenergy’ refers to the numerous forms
of biomass used for generating energy in the form of
fuel, electricity or heat. Biofuels like ethanol, biodiesel and biogas are produced through conversion of
plant materials that are rich in starch (e.g. maize) or
oils (e.g. oil palm, oilseed rape). Woody vegetation is
naturally the most traditional form of bioenergy and,
until about a century ago, biomass used for heating
and cooking was the biggest energy source globally.
With the accelerated use of fossil fuels, especially
in the industrialised world, the contribution of bioenergy had declined drastically since then, but over
recent years, climate change mitigation policies (see
chapter 2 and 4) have promoted the use of bioenergy. As a consequence, in countries and regions like
China, the EU, the US and Brazil, bioenergy production has increased up to threefold since the beginning of the 21st century.
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How much of the total global energy demand could
be supplied from plants is difficult to assess. Optimistically, up to 400 Exajoules (EJ) per year could be
reached by 2050. This number is fairly meaningless
to most people, but such an energy supply through
biological sources would be equivalent to two
thirds, or even more, of the present annual global
primary energy production. But other assessments
use a much lower value (around 100 EJ per year).
Underlying this wide range are uncertainties as to
how much energy could be derived from biomass
sources, which depend on assumptions about the future development of plant productivity, the efficiency of converting plant materials into different forms
of fuels, and uncertainties regarding the area of land
available for biomass production.
The promotion of bioenergy for climate change
mitigation is based on the notion of a closed cycle; only carbon that has been taken up during the
plant’s growth is released during the conversion and
combustion. However, studying the climate effect
of bioenergy should include consideration of the
energy required to convert plant materials into liquid or gaseous forms or aerosol particles that are
a by-product of combustion. Most critically, N2O
emissions from nitrogen fertilizers appear to affect
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the greenhouse balance of bioenergy more than initially thought, especially in intensively produced biofuel crops such as sugar cane or maize.
Concerns have also been raised that bioenergy production, especially biofuels generated from starch
and sugar crops, compete directly with food production and, in this way, contribute to high food
prices and accelerate natural land conversion. A
study that investigated the land-area needed for the
growth biomass either converted into biofuels or
used for electricity generation found that cars using
electricity travel, on average, 80% further than cars
fuelled by liquid biofuels for the same area of land.
Enhanced use of bioenergy from purpose-grown
biomass crops can thus lead to land-use change, including so-called indirect land-use change, when new
areas for food production are established elsewhere
to compensate for the reduced food production in
a given region.
of using plant biomass for energy production. The
negative impacts can be drastically reduced by the
use of by-products rather than purpose-grown bioenergy. When done carefully, bioenergy production
and food production can co-exist successfully, and
can be beneficial for rural development and rural
incomes.
Both direct and indirect land-use change can lead to
a loss of carbon stored in the original vegetation and
soils, which counteracts the CO2 emissions saved
through the combustion of bioenergy instead of fossil energy. This effect depends critically on the type
of ecosystem that is converted, and the efficiency
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7
How will land-based sectors
adapt to climate change?
Mark Rounsevell
Since the first establishment of the scientific evidence for climate change, there has been a political focus on reducing greenhouse gas emissions to
mitigate the problem (see chapter 2). Increasingly,
however, the realisation has come that the world is
already committed to some level of climate change,
which leads to the need to understand climate
change impacts, and to plan for adaptation to these
impacts. There are many ways in which individuals
and societies can adapt to climate change, some of
which can lead to opportunities and multiple benefits.
Different types of land managers have different ways
in which they could adapt to a changing climate. For
agriculture, this includes shifting to more heat-tolerant crop varieties, or changing crop sowing and
harvesting dates to better correspond with changing
weather patterns. Farmers can even modify the agricultural system itself (e.g. from grassland to crop
cultivation) through land-use change. Diversifying
the number and types of crops cultivated can also
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minimise the risks associated with a more variable
climate, which in itself would have potential benefits
for nature, in creating a wider range of habitats for
natural species. Farmers can also adapt to warmer and drier conditions by introducing irrigation
schemes, especially if these involve on-farm water
harvesting and storage, which minimises the impact
on the wider hydrological system through river and
groundwater abstraction. Indeed, warmer conditions may even lead to greater opportunities for
some land managers, for example by increasing the
potential for viticulture and wine production as well
as the production of other fruits at higher latitudes.
Likewise for forest managers, warmer conditions at
higher latitudes offer the potential to introduce a
wider range of tree species, provided the need to do
so is anticipated sufficiently early, since trees have
very long rotation times commensurate with the
rate of future climate change. In natural areas, biodiversity can be helped in adapting to climate change
by physically moving less mobile species from one
location to another (known as species translocation). Nature managers can also enhance the connectivity of existing nature reserves through the development of ecological corridors (known as green
infrastructure). Flooding is a major potential impact
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of climate change, but the re-establishment of natural wetlands can guard against future climate-mediated flood events (by acting as a buffer for excess
water) as well as provide new conditions for wetland species such as migratory birds. This type of
win-win situation can be implemented both in riverine systems and along the coast, where re-aligning coastlines through managed retreat involves removing sea walls and using saltmarsh vegetation as a
natural barrier to coastal flooding and sea level rise.
All of these examples of adaptation rely on individuals, or the broader communities within which they
live, anticipating the potential impacts of climate
change and implementing appropriate response
strategies. This requires prior knowledge of climate
change impacts, but also a willingness to engage in
long-term land management strategies of benefit to
everyone.
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8
Sustainable Land Use: Elinor
Ostrom’s Alternative
Mechtild Agreiter
“The road we have long been traveling is deceptively
easy, a smooth superhighway on which we progress
with great speed but at its end lies disaster. The other fork of the road -- ‘the one less travelled by’ -- offers our last, our only chance to reach a destination
that assures the preservation of our earth.”
Rachel Carson made this statement in 1962, in her
book Silent Spring. Already, she could see that “we
are being asked to take senseless and frightening
risks”. Carson believed that we should take responsibility and identify for ourselves the other paths
available to us. What could this mean in the context
of land use and climate change?
strated that technical solutions are not enough
without the crucial step of altering human social
behaviour. Instead of looking to nationalization and
privatization, she envisaged a third option: the possibility of a co-operative approach, even within complex systems. In 2009 she became the first woman
to win the Nobel Prize in Economic Sciences, for
her research in the field of sustainable use of common resources (or ‘commons’). The value of her
work lies in the evidence that the commons need
not, and must not, be used in an economically and
ecologically destructive manner. Through multiple
studies, Ostrom has shown that the participants can
find successful rules for collective and sustainable
land use.
Ostrom outlines eight ‘design principles’ that could
be viewed as instructions for the use of a commons
such as land and/or climate.
Land use today, alongside our rapidly changing climate, poses challenges for us that we often try to
meet with technical innovations. In doing so, such
challenges deceptively appear simply as a question
of natural sciences, with little or nothing to do with
human values and ethics and, consequently, social
change. Elinor Ostrom has emphatically demon56
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Elinor Ostrom’s design principles for the
successful and sustainable management of a
commons:
1.
2.
3.
4.
5.
6.
7.
8.
Clearly defined boundaries
Coherence with local needs and conditions
Collective decision-making
Monitoring of users and resources
Scale of graduated sanctions for rule violators
Conflict resolution processes
Recognition of rights
Polycentric structure of governance, with nested (accountable) institutions
Ostrom’s assumption is that people will voluntarily
abide by such rules in specific local contexts, and
that they will look beyond their own maximum benefit, especially when this can resolve social conflict.
Such a system could also work in the context of
climate change and land use. The crucial point, as
underlined by Ostrom, is that people take responsibility and organise themselves, working together to
find solutions that take into account local needs and
conditions, and involve all stakeholders.
One of the biggest challenges for such a system is
to create the conditions for successful implementation; for a sustainable self-organisation of actors, or
for a genuine voice for individuals, that increases the
sense of (collective) responsibility and thus leads to
a more sustainable use of the land resource.
When considering the deforestation of rainforests
or the massive so-called ‘land grabbing’ of the last
years, with its often devastating effects, it is clear
that land use could be seriously, and positively, altered, as a result of applying Ostrom’s principles.
The establishment of multiple small initiatives in
many places of the world could make more sense
than waiting for globally-organised remedies or in-
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ternational conventions. It is self-evident that this
proposed system should be supported by policy. As
the Nobel Committee stated, the future of the people belongs to “the organization of cooperation”.
For such change to succeed, the focus must be shifted onto people, rather than technical advancements
and the selective interests of the few. Rapid action is
required, especially when considering the advancement of climate change, global social disparities, and
world hunger.
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Contributors:
Prof. Dr. Detlef van Vuuren
Dr. Elke Stehfest
Prof. Dr. Almut Arneth
Department of Climate, Air and Energy, PBL Netherlands Environmental
Dr. Mechtild Agreiter
Assessment Agency
Dr.Thomas Pugh
http://www.pbl.nl/en/aboutpbl/departments/climate-air-and-energy
Karlsruhe Institute of Technology (KIT), Institute of Meteorology and
Climate Research, Atmospheric Environmental Research (IMK-IFU), Gar-
Ms Kerstin Baumans
misch-Partenkirchen, Germany
Lund University, Dept. Physical Geography and Ecosystem Science, Swe-
http://imk-ifu.fzk.de/plant_atmosphere_interactions.php
den
http://www.nateko.lu.se
Dr. Joanna House
Cabot Institute School of Geographical Sciences, University of Bristol, UK
Prof. Mark Rounsevell
http://www.bristol.ac.uk/geography
David Kinloch Michie Chair of Rural Economy and Environmental Sustainability, School of GeoSciences, University of Edinburgh, UK
Dr. Annalisa Savaresi
http://www.ed.ac.uk/schools-departments/geosciences
Edinburgh Law School, University of Edinburgh, UK
http://www.law.ed.ac.uk/
Nathalie de Noblet-Ducoudré
Picture credits
Laboratoire des Sciences du Climat et de l’Environnement, Centre na-
© S. Rösner | pixeldiversity.com (cover; p. 1; 4; 36/37; 49; 58; 59), © Almut
tional de la recherche scientifique, France
Arneth (p. 2; 15; 31), © Delphine Deryng (p. 7), © Anita Bayer/DLR (p. 8/9),
http://www.lsce.ipsl.fr
© Nadine Rühr (p. 19), © Andreas Gast (p. 25; 38/39; 44/45; 49; 53), © Ines
Bamberger (p. 56; 62/63)
Dr. Alexander Popp
Potsdam Institute for Climate Impact Research, Germany
Figures
https://www.pik-potsdam.de
Almut Arneth (p. 16/17);Thomas Pugh (p. 22); Nathalie de Noblet & Almut
Arneth (p. 30)
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This booklet was written as part of the project LUC4C, Landuse change: assessing the net climate forcing, and options for climate change mitigation and adaptation, funded by the European
Commission in its 7th Framework Programme. In it, you will
find short articles about the interaction of land-use change and
climate change, climate policy, the state of the art of climate
models and scenarios, the connection to food production and
the interaction with human societies.
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